It is known that a valve timing controller adjusts valve timing of an internal combustion engine by utilizing an electric motor or an electromagnetic brake. JP-2005-146993A shows a valve timing controller in which a relative phase difference between a crankshaft and a camshaft is maintained at a middle phase between the most advance phase and the most retarded phase in order to improve a startability and performance of the engine. In this valve timing controller, a sub-brake is provided besides an electromagnetic brake. The electromagnetic brake applies a brake torque from a brake shaft to a phase-changing mechanism in order to change the relative phase difference. The sub-brake is operated when the engine is turned off. The middle phase is obtained by a torque balance between the sub-brake and a spring provided in the phase-changing mechanism.
In this valve timing controller, a cam torque applied to the brake shaft from the camshaft is likely to vary in a large amount according to a temperature condition when the engine is operated at a low speed. It is relatively difficult to adjust the torque balance with high accuracy. Hence, the accuracy of the middle phase is deteriorated, so that it may be hard to start the engine properly.